This invention relates generally to magnetic resonance imaging (MRI), and more particularly the invention relates to imaging a dynamic object in which a field of view includes both a dynamic portion and a static portion during a motion cycle. The invention and background will be described with reference to publications listed in the attached appendix.
Several MRI applications involve imaging a dynamic object to resolve its temporal behavior [1-8]. In such applications, it is often difficult to achieve the desired temporal resolution while maintaining the required spatial resolution and field-of-view (FOV). Methods have been developed to increase the temporal resolution in the special case where only a fraction of the FOV undergoes fully dynamic changes [9, 12], the rest of the FOV being considered fully static [9, 11], undergoing a cyclic motion [10], or just being xe2x80x98less dynamicxe2x80x99 than the fully dynamic part [12]. Although cardiac imaging is an important example of an imaging application where motion is concentrated into only a part of the FOV, the reduced-FOV (rFOV) methods mentioned above are not compatible with one of the most common cardiac sequences, so-called xe2x80x98retrospectivexe2x80x99 cine imaging [1, 2]. Because of the time interpolation involved in cine reconstruction, one cannot change the sampling function from time frame to time frame as is done in [11, 12], or acquire only one or a few full FOV images as is done in [9, 10].
The present invention is a rFOV method designed to be compatible with cine imaging, providing an increase by a factor n in temporal resolution (or a decrease by a factor n in scan time) if only 1/nth of the FOV is dynamic, the rest being considered static.
With the present method, only a fraction of all the k-space xe2x80x98portionsxe2x80x99 (e.g. lines) need to be acquired multiple times over a full cardiac cycle (instead of all the k-space xe2x80x98portionsxe2x80x99, as in normal CINE imaging). It is shown that if only one nthof the FOV is dynamic, only one nth of the k-space xe2x80x98portionsxe2x80x99 need to be acquired multiple times. The remaining fraction ((nxe2x88x921)/n) of the k-space xe2x80x98portionsxe2x80x99 can be acquired only once, leading to an increase by about a factor n in temporal resolution or a decrease by about n in scan time. Using the data acquired multiple times, along with the assumption that only one nthof the FOV is dynamic, it is shown that values for the xe2x80x98portionsxe2x80x99 acquired only once can be calculated for any cardiac phase. Accordingly, there is no need to acquire this data at multiple cardiac phases. Avoiding the acquisition of such unnecessary data leads to the stated increase in temporal resolution, or decrease in scan time.
The invention and objects and features thereof will be more readily apparent from the following description and appended claims when taken with the drawings.